Zwitterionic Phosphorus Ylide Adducts of Boron‐Bridged ansa ‐Zirconocene Complexes as Precatalysts for Olefin Polymerization

Methylenetriphenylphosphorane was coordinated to the boron of phenylborylidene‐bridged bis(cyclopentadienyl)‐ and bis(2‐Me,4‐Ph‐indenyl)zirconium dichloride to form zwitterionic ansa ‐zirconocene complexes. The cyclopentadienyl complex 2 , when activated with MAO, exhibits remarkable polymerization activity that is more than an order of magnitude greater than that of a related amidoborylidene‐bridged complex as well as the commercially important precatalyst [Cp′−SiMe 2 − N − t Bu]TiCl 2 (Cp′ = C 5 Me 4 ). The zwitterionic bis(2‐Me,4‐Ph‐indenyl)zirconium dichloride species is isolated as a mixture of rac and meso isomers 4 − 6 . The propylene polymerization efficiency of the isomer mixture activated by MAO is greater than that of a related silylene bridged system at 70 and 85 °C; however, the activity of the zwitterionic system decreased with further increase in temperature. The high level of isotactic triads (63.6%) and pentads (52.4%) in the polypropylene formed by 4 − 6 indicates that the rac isomer is the most active precatalyst of the mixture. The molecular structures of 2 and the rac bis‐indenylzirconium isomer 4 and one of the meso isomers 5 are described. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)